The invention is based on a fuel injection pump as set forth hereinafter. In one such fuel injection pump, known from German Published, Nonexamined Patent Application DE-OS 24 58 109, the control of the pressure in the pressure chamber enclosed in the cylinder by the injection adjuster piston is accomplished by a 2/3-way valve, which makes the pressure chamber communicate with either a pressurized oil feed pump or with a relief line. By means of the pressurized oil fed into the pressure chamber, the injection adjuster piston is displaced counter to the force of the spring, and the injection onset of the associated fuel injection pump is adjusted accordingly. The control is effected such that the injection adjuster piston is adjusted, by suitable actuation of the 2/3-way valve, between a first position that opens the relief line and a second position that opens the pressure line. In an alternative embodiment, cell chambers that receive pressurized oil are provided between a driving device and a driven device of the fuel injection pump, whose communication with an oil feed pump or a relief conduit is controlled by a 2/4-way valve. In one position of the 2/4-way valve, fuel is delivered from the oil feed pump to one of the pressure chambers, and taken from the other of the pressure chambers via a relief line. If the position of the 2/4-way valve changes, the delivery and removal of fuel take place in reverse order. Also with this device, in the known version, two different positions of the drive device relative to the driven device can be established. By comparison, it is also necessary, in accordance with the predetermined operating parameters, to set intermediate positions precisely and also adhere to them.
The fuel injection pump according to the invention has the advantage over the prior art that by the embodiment of the valve member of the control valve as a slide, it is possible, with only slight adjusting forces, to control an exact control of the inflow to or outflow from the pressure chamber. In particular by closure of the connecting line by the control collar of the slide, a previously set positioning of the injection adjuster piston can be maintained. By closure of the connecting line, the restoring forces that occur in the respective pump piston pumping stroke of the fuel injection pump and are transmitted by the cam ring to the injection adjuster piston are also intercepted, since the volume that is enclosed by the injection adjuster piston in the cylinder is embodied, with the cooperation of the control valve, as a closed volume, and only a deflection of the injection adjuster piston, within the scope of the elastic compressibility of the enclosed hydraulic column, is realized. At the end of a respective pumping stroke of the pump pistons of the fuel injection pump, the injection adjuster piston assumes the previously desired position, and thus controls the recurring injection onset in the desired exact way. At most, if a change in the injection onset is necessary in the meantime because of correspondingly altered operating parameters, the pressure in the pressure chamber can be varied by opening the pressure chamber to the pressure source or to the relief line. With the aid of the control slide, it is furthermore possible to establish overflow cross sections of different sizes between the connecting line and pressure line or relief line, so that the rate of pressure change in the pressure chamber can be variably high, depending on the triggering of the control valve. The result is highly flexible control, by which as needed a desired fast and a desired major injection onset adjustment can be attained. Advantageously, the adjustment of the valve slide is effected by an electromagnet, which adjusts the valve slide in analog fashion or proportionately to a control value. In an alternative version, the control slide can also be triggered in clocked fashion, which lessens the friction of repose, which counteracts adjustment, upon a deflection out of relatively long-maintained steady positions of the valve slide.
Because the cam slide has two collars, that is, a control collar and guide collar, the can slide is acted upon hydraulically in the axial direction by forces of equal magnitude, so that the slide is displaced by the electromagnet solely counter to the force of a restoring spring, in accordance with claim 3. In an advantageous refinement both the pressure chamber that is located on one face end of the injection adjuster piston and a second pressure chamber, which is located on the opposite face end of the injection adjuster piston, are acted upon continuously with pressure fluid by means of the control valve, in that the pressure in these pressure chambers, given a suitable design of the control valve slide, is controlled in complementary fashion by control of the flow of pressure fluid. The control slide is advantageously equipped with two control collars, which in a middle position close the respective connecting lines between the control valve and the pressure chambers on the injection adjuster piston, so that the injection adjuster piston assumes a neutral position, which has been preset beforehand by the appropriate triggering of the control valve. If operating parameters change, then a fast, efficient adjustment of the injection adjuster piston can be brought about by delivering pressure fluid to one pressure chamber and removing pressure fluid from the other pressure chamber. In this case, the speed of adjustment of the injection adjuster piston can also be increased.
It is common to all the exemplary embodiments that the delivery of pressure fluid can be made directly into the pressure chambers, without radially stressing the injection adjuster piston. This reduces the frictional forces and wear of the injection adjuster piston and its guide and assures a long service life. Because of the direct feeding in of pressure fluid and a re-closure of the pressure chambers by the control slide, a minimum demand for pressure fluid is adhered to. High adjustability is possible even at low rpm of the fuel injection pump, which drives a pressure fluid pump in accordance with this rpm, since the outflow losses are minimized. Particularly in a version in which in one of the pressure chambers, in addition to the feeding in of pressure fluid, a restoring spring is also provided, the injection adjuster piston can assume a preferential position for the injection onset adjustment even while the pressure fluid feed quantities are not yet ready, and engine starting is correspondingly promoted as a result. In this position, the pressure chambers are advantageously closed by the control slide, and the injection onset adjuster piston has moved into the aforementioned preferential position under the influence of this spring and enabled by the leakage losses at the circumference of the injection adjuster piston.
In an especially advantageous way, it is possible to make a recess in the injection adjuster piston, which allows a coupling part, which is connected to the cam drive, to be introduced so far into the injection adjuster piston that the contact face between the coupling part and the injection adjuster piston is located in a region that is substantially in the injection adjuster piston axis. The restoring forces of the cam drive are thus directed axially to the injection adjuster piston, and exposure of the injection adjuster piston to tilting moments is averted. In an advantageous refinement according to claim 11, the contact face can be disposed slightly offset from the injection adjuster piston axis, which has the advantage that in this way an automatic self-alignment of the injection adjuster piston with the coupling part is assured, so that the axis of the recess remains set substantially in coincidence with the axis of the coupling part.